The present invention relates to an element for lighting rooms by selective daylight guidance, comprising an optically transparent main body through which the light is incident into the respective room, as well as to a method of manufacturing such an element.
A very high importance must be attached to an appropriate illumination with daylight in the working and living environment of man. Daylight used better than this is usual with normal windows would not only result in an improved well-being and a higher productivity in work but would also lead to substantial savings in energy. Architects and illumination designers attempt to take these facts into consideration to an ever-increasing extent with various provisions.
A substantial contribution can be achieved with window elements which deflect the light which is available at a high level on the facade selectively into the interior of the rooms beyond the normal measure.
At present prism elements, holographic systems or the like are being used for such light or window elements.
From the German Patent DE 195 38 651 A1, for example, a sun shade device is known which consists of a material transparent to sunlight and which has a planar configuration and a smooth surface which is irradiated by the light. The underside presents at least one prism-type contour having a cross-section including an approximately rectangular triangle.
The known elements hence require the application of expensive main bodies which must then be further processed at a comparatively high expenditure so that they have so far not been widely accepted.
The present invention is based on the problem of proposing an element for lighting rooms by the selective guidance of daylight, which presents a high optical efficiency in terms of its function and which can be manufactured at reasonable costs.
Moreover, the invention is intended to propose a method of producing such an element.
One inventive element is defined in claim 1. Improvements of this method are the subject matter of claims 2 and 3.
One inventive method of manufacturing such elements is defined in claim 4. Improvements of this method are defined in claims 5 et seq.
In the element characterized in claim 1 a plurality of structure is provided in the optically transparent main body, on which (additional) light is deflected into the respective room by total reflection. The plurality of structures may consist of parallel crazes.
The term xe2x80x9ccrazesxe2x80x9d is to be understood to denote flat wedge-shaped deformation centers producing a variation of the refractive index relative to the basic material, such as those which can be generated in vitreous or glass-like thermoplastic materials in particular. Crazes, i.e. flat wedge-shaped deformation centers, are created on locally excessive stress peaks such as those which occur on the tips of fissures, for instance. Macroscopically they have the appearance of small fissures and propagate in a direction normal on the main direction of tensile stress, just like fissures.
In this concept it is especially important that the refractive index is reduced relative to the index of the basic polymer material whilst at the same time the transition from the basic material to the craze is distinct so that total the transition from the basic material to the craze is distinct so that total reflections are achieved on the crazes, which guide additional light reflections are achieved on the crazes, which guide additional light through the window pane into the respective room to be lighted.
The thermoplastic material may be polymethylmethacrylate (PMMA) in particular. Besides this material, however, other polymers such as polystyrene, polycarbonate etc. may be employed on the condition that they are transparent and that they are suitable for generating the inventive structures therein for supplying additional light into the respective room.
In the inventive method of manufacturing an element for lighting rooms by selective guidance of (additional) daylight, which is appropriate in particular for producing an element according to any of the claims 1 to 4, a plate-shaped main body consisting of a polymer is subjected to a tensile stress applied in parallel with the surface of the plate. This gives rise to the formation of so-called crazes in particular, i.e. flat wedge-shaped deformation centers presenting a refractive index at variance from the index of the basic material.
What is particularly preferred is the concept that during the application of the tensile stress a solvent and especially an organic solvent is additionally applied on the plate surface. The organic solvent is a polar solvent and preferably acetone, ethanol or methanol.
The application of stress and possibly of a solvent can preferably be performed at an elevated temperature below both the glass transition temperature of the polymer material and the boiling temperature of the solvent.
The inventive method is also suitable for processing continuous material webs:
In such a concept it is preferred that a bending device is used to apply or create the tensile stress, through which the plate material is passed in the form of a continuous material web. The principle of the bending device is that bending is applied simultaneously at four points of the plate material by means of rotating cylinders as loading means.